Cyanic acid ester compounds form triazine rings by curing and are widely used as starting materials for various functional polymer materials such as composite materials for structures, adhesives, electrical insulating materials, and electric and electronic components, because of their high heat resistance and excellent electrical properties. In recent years, however, stricter physical properties have been demanded for functional polymer materials with a higher level of required performance in these fields of application. Examples of such physical properties include flame retardance, heat resistance, low rates of thermal expansion, low water absorbability, low permittivity, low dielectric loss tangent, weather resistance, chemical resistance, and high fracture toughness. However, these required physical properties have not always been satisfied so far.
For example, in the field of semiconductor packaging materials, undesired warpage occurs due to the mismatched coefficient of thermal expansion between semiconductor chips and substrate materials with thinning of substrates. As an approach for solving this problem, the functional polymer materials themselves for use in substrate materials are required to have lower thermal expansion and higher heat resistance. Furthermore, use of lead-free solder is promoted for the soldering of printed circuit boards, in consideration of human bodies and environments. In response to this, the functional polymer materials themselves are also required to have lower thermal expansion and higher heat resistance because of being capable of resisting a reflow step at a high temperature.
Conventional functional polymer materials may be allowed to contain a halogen atom or a phosphorus atom from the viewpoint of enhancing the flame retardance of the functional polymer materials. However, the halogen atom has the possibility of generating halogenated gases, which might cause environmental pollution, during combustion. In addition, the halogen atom reduces the insulating properties of final products. Also, the phosphorus atom often reduces the required physical properties (heat resistance, moisture resistance, and low water absorbability, etc.) except for flame retardance. Accordingly, there is also a demand for improving the flame retardance of the functional polymer materials without containing a halogen atom and a phosphorus atom.
In the case of producing a laminate for use in printed circuit boards, etc., first, monomers before curing are dissolved as functional polymer material precursors in a solvent such as methyl ethyl ketone to prepare varnish. Then, glass fiber is impregnated with this varnish and dried to prepare a prepreg. Therefore, there is also a demand for improving the solvent solubility of the monomers.
In the field of semiconductor encapsulation materials, studies have been actively conducted to replace silicon (Si) semiconductor devices with wide-gap semiconductors such as silicon carbide (SiC) semiconductors with the aim of reduction in power loss (energy saving). The SiC semiconductors are more chemically stable than the Si semiconductors and therefore permit operation at a high temperature exceeding 200° C. Thus, it can also be expected that apparatuses are miniaturized. In response to this, compositions comprising functional polymer materials for use in encapsulation materials are required to have heat resistance, low thermal expansion, and heat resistance at high temperatures over a long period (hereinafter, referred to as long-term heat resistance), etc.
Use of a bifunctional cyanatophenyl-type cyanic acid ester compound in which hydrogen of a methylene group that bonds cyanatophenyl groups is replaced with a particular alkyl group (1,1-bis(4-cyanatophenyl)isobutane) has been proposed as an example of obtaining a cured product of a cyanic acid ester compound alone which possesses low thermal expansion and heat resistance (see Patent Literature 1). However, for the bifunctional cyanatophenyl-type cyanic acid ester compound, the flame retardance (persistency at high temperatures) is reduced by replacing hydrogen of the methylene group that bonds cyanatophenyl groups with an alkyl group. Moreover, Patent Literature 1 has no mention about flame retardance and long-term heat resistance.
Use of a cyanic acid ester compound having an aralkyl structure has been proposed as an example of obtaining a cured product of a cyanic acid ester compound alone which possesses low thermal expansion and flame retardance (see Patent Literature 2). However, the cyanic acid ester compound having an aralkyl structure is poorly soluble in a solvent and is thus difficult to handle.
In addition, use of an isocyanuric acid skeleton-containing cyanic acid ester compound (see Patent Literature 3), a triazine skeleton-containing cyanic acid ester compound (see Patent Literature 4), a bifunctional cyanatophenyl-type cyanic acid ester compound in which hydrogen of a methylene group that bonds cyanatophenyl groups is replaced with a biphenyl group (see Patent Literature 5), and a cyanation product of a phenol-modified xylene formaldehyde resin (see Patent Literature 6), a combination of a trifunctional cyanatophenyl-type (trisphenolalkane-based) cyanic acid ester compound and a bifunctional cyanatophenyl-type cyanic acid ester compound (see Patent Literature 7), and a combination of a bisphenol A-based cyanic acid ester compound and an imide skeleton-containing cyanic acid ester compound (see Patent Literature 8) have been proposed as examples of obtaining a cured product of a cyanic acid ester compound alone which possesses flame retardance and/or heat resistance. However, all of these literatures have no mention about the rate of thermal expansion, long-term heat resistance, and/or solvent solubility.